identifier: METPO:1000806
label: Disproportionation
definition: A metabolism in which a single substrate simultaneously undergoes both
  oxidation and reduction reactions, with part of the substrate serving as the electron
  donor and another part serving as the electron acceptor.
definition_source: DOI:10.1080/17415990802105770
trait_category: METABOLISM
term_kind: CLASS
mapping_status: REVIEWED
parent_traits:
- METPO:1000060
created_by: Jed Dongjin Kim-Ozaeta
evidence:
- reference: DOI:10.1080/17415990802105770
  snippet: serve as both electron donor and acceptor
  notes: Review supports inorganic sulfur disproportionation as one substrate serving
    both donor and acceptor roles.
- reference: DOI:10.1016/j.gca.2013.03.013
  snippet: elemental sulfur disproportionation
  notes: Study supports elemental sulfur disproportionation in acidophilic microbial
    metabolism.
canonical_examples:
- taxon_id: NCBITaxon:65555
  taxon_label: Desulfocapsa sulfexigens
  note: "Model for inorganic-sulfur disproportionation (S0/thiosulfate/sulfite to sulfate + sulfide as sole energy source)."
  reference: PMID:23961312
causal_graphs:
- graph_id: sulfur_disproportionation_redox_split
  title: Sulfur disproportionation redox split
  description: DOI-backed graph linking a single sulfur intermediate to simultaneous
    oxidation and reduction products under anoxic conditions.
  nodes:
  - node_id: disproportionation_trait
    label: Disproportionation
    node_type: TRAIT
    grounding: METPO:1000806
    description: Metabolism in which one substrate is both oxidized and reduced.
  - node_id: anoxic_condition
    label: anoxic condition
    node_type: ENVIRONMENTAL_FACTOR
    description: Oxygen-free condition for many microbial sulfur disproportionation
      processes.
    grounding: PATO:0001456
  - node_id: inorganic_sulfur_intermediate
    label: inorganic sulfur intermediate
    node_type: CHEMICAL
    description: Sulfur compound that can act as both electron donor and acceptor.
  - node_id: elemental_sulfur
    label: elemental sulfur
    node_type: CHEMICAL
    description: Representative sulfur disproportionation substrate.
    grounding: CHEBI:26833
  - node_id: thiosulfate
    label: thiosulfate
    node_type: CHEMICAL
    description: Representative sulfur disproportionation substrate.
    grounding: CHEBI:16094
  - node_id: sulfide
    label: sulfide
    node_type: CHEMICAL
    description: Reduced sulfur product.
    grounding: CHEBI:15138
  - node_id: sulfate
    label: sulfate
    node_type: CHEMICAL
    grounding: CHEBI:16189
    description: Oxidized sulfur product.
  - node_id: reverse_sulfate_reduction_pathway
    label: reverse sulfate reduction pathway
    node_type: PATHWAY
    description: Enzymatic route proposed for some sulfur disproportionators.
  - node_id: tetrathionate
    label: tetrathionate
    node_type: CHEMICAL
    description: S4-intermediate (S4O6 2-) produced from thiosulfate oxidation in
      the S4I pathway.
  - node_id: sulfite
    label: sulfite
    node_type: CHEMICAL
    description: Sulfur oxyanion product of elemental sulfur disproportionation by
      SOR.
  - node_id: tsda_thiosulfate_dehydrogenase
    label: TsdA thiosulfate dehydrogenase
    node_type: GENE_OR_PROTEIN
    description: Enzyme oxidizing thiosulfate to tetrathionate, entry step of the
      S4 intermediate pathway.
  - node_id: teth_tetrathionate_hydrolase
    label: TetH tetrathionate hydrolase
    node_type: GENE_OR_PROTEIN
    description: Enzyme that hydrolyzes/disproportionates tetrathionate to elemental
      sulfur, thiosulfate, and sulfate.
  - node_id: sor_sulfur_oxygenase_reductase
    label: SOR sulfur oxygenase reductase
    node_type: GENE_OR_PROTEIN
    description: Enzyme catalyzing O2-dependent disproportionation of elemental sulfur
      into sulfite and sulfide.
  - node_id: iron_sulfide_mineral
    label: iron-sulfide mineral formation
    node_type: CHEMICAL
    description: Fe-sulfide mineral (e.g., FeSx) formed when produced sulfide is scavenged,
      removing inhibitory sulfide.
  edges:
  - subject: disproportionation_trait
    predicate: occurs in
    object: anoxic_condition
    description: Sulfur disproportionation is commonly observed as anaerobic microbial
      metabolism.
    evidence:
    - reference: DOI:10.1080/17415990802105770
      snippet: microbiologically catalyzed chemolithotrophic process
      notes: Supports microbial sulfur disproportionation under non-oxygenated sulfur
        cycling contexts.
    predicate_id: biolink:occurs_in
  - subject: inorganic_sulfur_intermediate
    predicate: serves as electron donor and acceptor
    object: disproportionation_trait
    description: A single sulfur intermediate provides both donor and acceptor halves.
    evidence:
    - reference: DOI:10.1080/17415990802105770
      snippet: serve as both electron donor and acceptor
      notes: Directly supports the defining redox split.
    predicate_id: METPO:2007603
  - subject: elemental_sulfur
    predicate: example of
    object: inorganic_sulfur_intermediate
    description: Elemental sulfur is a disproportionation substrate.
    evidence:
    - reference: DOI:10.1016/j.gca.2013.03.013
      snippet: elemental sulfur disproportionation
      notes: Supports elemental sulfur as a substrate.
    predicate_id: rdfs:subClassOf
  - subject: thiosulfate
    predicate: example of
    object: inorganic_sulfur_intermediate
    description: Thiosulfate is a disproportionation substrate.
    evidence:
    - reference: DOI:10.1080/17415990802105770
      snippet: elemental sulfur, thiosulfate, and sulfite
      notes: Supports thiosulfate among disproportionated sulfur intermediates.
    predicate_id: rdfs:subClassOf
  - subject: inorganic_sulfur_intermediate
    predicate: reduced to
    object: sulfide
    description: One fraction of the substrate is reduced to sulfide.
    evidence:
    - reference: DOI:10.1080/17415990802105770
      snippet: generate hydrogen sulfide and sulfate
      notes: Supports sulfide as reduced product.
  - subject: inorganic_sulfur_intermediate
    predicate: oxidized to
    object: sulfate
    description: One fraction of the substrate is oxidized to sulfate.
    evidence:
    - reference: DOI:10.1080/17415990802105770
      snippet: generate hydrogen sulfide and sulfate
      notes: Supports sulfate as oxidized product.
    predicate_id: METPO:2007405
  - subject: reverse_sulfate_reduction_pathway
    predicate: participates in
    object: disproportionation_trait
    description: Some disproportionating microbes use reversed sulfate-reduction enzymes.
    evidence:
    - reference: DOI:10.1080/17415990802105770
      snippet: reverse the sulfate reduction pathway
      notes: Supports the proposed pathway mechanism for some isolates.
    predicate_id: biolink:participates_in
  - subject: thiosulfate
    predicate: produces
    object: sulfate
    description: Thiosulfate disproportionation yields sulfate as the oxidized product.
    evidence:
    - reference: DOI:10.1128/msystems.00954-22
      notes: Thiosulfate disproportionation follows the stoichiometry S2O3(2-) + H2O
        -> SO4(2-) + HS- + H+.
    predicate_id: METPO:2000202
  - subject: thiosulfate
    predicate: produces
    object: sulfide
    description: Thiosulfate disproportionation yields sulfide as the reduced product.
    evidence:
    - reference: DOI:10.1128/msystems.00954-22
      notes: Thiosulfate disproportionation follows the stoichiometry S2O3(2-) + H2O
        -> SO4(2-) + HS- + H+.
    predicate_id: METPO:2000202
  - subject: tsda_thiosulfate_dehydrogenase
    predicate: catalyzes oxidation of
    object: thiosulfate
    description: TsdA oxidizes thiosulfate to tetrathionate, the entry step of the
      S4 intermediate pathway.
    evidence:
    - reference: DOI:10.3389/fmicb.2024.1426584
      notes: tsdA (and doxDA) catalyze conversion of thiosulfate (S2O3 2-) to tetrathionate
        (S4O6 2-).
  - subject: tsda_thiosulfate_dehydrogenase
    predicate: produces
    object: tetrathionate
    description: Product of TsdA-catalyzed thiosulfate oxidation is tetrathionate.
    evidence:
    - reference: DOI:10.3389/fmicb.2024.1426584
      notes: tsdA catalyzes conversion of thiosulfate to tetrathionate (S4O6 2-).
    predicate_id: METPO:2000202
  - subject: teth_tetrathionate_hydrolase
    predicate: disproportionates
    object: tetrathionate
    description: TetH hydrolyzes/disproportionates tetrathionate into elemental sulfur,
      thiosulfate, and sulfate.
    evidence:
    - reference: DOI:10.3389/fmicb.2024.1426584
      notes: Tetrathionate can be subsequently disproportionated via tetH to form
        S0, S2O3 2-, and SO4 2-.
    predicate_id: METPO:2000200
  - subject: sor_sulfur_oxygenase_reductase
    predicate: disproportionates
    object: elemental_sulfur
    description: SOR catalyzes disproportionation of elemental sulfur, releasing sulfite
      and sulfide.
    evidence:
    - reference: DOI:10.1007/978-3-031-54306-7_15
      notes: The SOR catalyzes an O2-dependent S0 disproportionation releasing SO3
        2- and HS-.
    predicate_id: METPO:2000200
  - subject: sor_sulfur_oxygenase_reductase
    predicate: produces
    object: sulfite
    description: Sulfite is the oxidized product of SOR-catalyzed elemental sulfur
      disproportionation.
    evidence:
    - reference: DOI:10.1007/978-3-031-54306-7_15
      notes: SOR catalyzes an O2-dependent S0 disproportionation releasing SO3 2-
        and HS-.
    predicate_id: METPO:2000202
  - subject: iron_sulfide_mineral
    predicate: scavenges
    object: sulfide
    description: Formation of Fe-sulfide minerals scavenges produced sulfide, relieving
      product inhibition of sulfur disproportionation.
    evidence:
    - reference: DOI:10.1128/msystems.00954-22
      notes: Ferrihydrite scavenges produced sulfide as Fe-sulfide.
curation_history:
- timestamp: '2026-05-05T01:35:46.914112+00:00'
  curator: seed_from_metpo
  action: SEEDED_FROM_METPO
  changes: imported from data/raw/metpo.owl (CLASS)
  llm_assisted: false
- timestamp: '2026-05-08T00:00:00-07:00'
  curator: codex
  action: ADDED_CAUSAL_GRAPH
  changes: Added DOI-backed causal graph for sulfur disproportionation substrates,
    donor/acceptor redox split, sulfide and sulfate products, and reverse sulfate-reduction
    pathway involvement.
  llm_assisted: true
- timestamp: '2026-05-20T05:49:24Z'
  curator: claude
  action: GROUND_CAUSAL_PREDICATES
  changes: Grounded 1 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv
    (biolink:participates_in×1).
  llm_assisted: true
- timestamp: '2026-05-23T08:21:49Z'
  curator: claude
  action: GROUND_CAUSAL_PREDICATES
  changes: Grounded 2 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv
    (rdfs:subClassOf×2).
  llm_assisted: true
- timestamp: '2026-05-23T21:30:06Z'
  curator: claude
  action: GROUND_CAUSAL_PREDICATES
  changes: Grounded 1 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv
    (METPO:2007405×1).
  llm_assisted: true
- timestamp: '2026-05-24T04:38:00Z'
  curator: claude
  action: GROUND_CAUSAL_NODES
  changes: Grounded 2 causal-node grounding field(s) via mappings/node_grounding.tsv
    (ENVO:01001057×1, CHEBI:15138×1).
  llm_assisted: true
- timestamp: '2026-05-24T08:14:32Z'
  curator: claude
  action: GROUND_CAUSAL_NODES
  changes: Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv
    (CHEBI:33542×1).
  llm_assisted: true
- timestamp: '2026-05-26T05:00:47Z'
  curator: claude
  action: RENAME_PREDICATE_LABELS
  changes: 'Renamed 1 causal-edge predicate label(s) to align with existing groundings:
    occurs under → occurs in ×1.'
  llm_assisted: true
- timestamp: '2026-05-26T05:00:50Z'
  curator: claude
  action: GROUND_CAUSAL_PREDICATES
  changes: Grounded 1 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv
    (biolink:occurs_in×1).
  llm_assisted: true
- timestamp: '2026-06-14T05:51:46Z'
  curator: claude
  action: GROUND_CAUSAL_NODES
  changes: Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv
    (CHEBI:26833×1).
  llm_assisted: true
- timestamp: '2026-06-14T07:26:19Z'
  curator: claude
  action: GROUND_CAUSAL_PREDICATES
  changes: Grounded 1 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv
    (METPO:2007603×1).
  llm_assisted: true
- timestamp: '2026-06-15T07:19:08Z'
  curator: claude
  action: FIX_NODE_GROUNDING_CURIE
  changes: Overwrote 2 causal-node grounding(s) to corrected CURIEs (phase-2 id-label
    fix; verified vs OAK).
  llm_assisted: true
- timestamp: '2026-06-23T00:00:00Z'
  curator: claude
  action: ENRICH_CAUSAL_GRAPH
  changes: Added 8 evidence-backed generic edges (6 new nodes) from the deep-research
    report.
  llm_assisted: true
- timestamp: '2026-06-24T17:21:12Z'
  curator: claude
  action: GROUND_CAUSAL_PREDICATES
  changes: Grounded 4 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv
    (METPO:2000202×4).
  llm_assisted: true
- timestamp: '2026-06-24T17:23:38Z'
  curator: claude
  action: GROUND_CAUSAL_PREDICATES
  changes: Grounded 2 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv
    (METPO:2000200×2).
  llm_assisted: true